SERVER-99508 Ensure that the $_internalUnpackBucket stage is generated exactly once for timeseries reads

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• Needs Scheduling

SERVER-99510 Ensure that the $_internalUnpackBucket stage can be generated before ClusterAggregate::runAggregate

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• Needs Scheduling

SERVER-100563 Ensure that $_internalUnpackBucket generation behaves correctly with special pipeline stages

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• Needs Scheduling

SERVER-100682 Implement and validate end-to-end tests as necessary for new timeseries read path

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• Backlog

SERVER-100560 Update timeseries documentation to include information about the new code path

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• Needs Scheduling